The present invention discloses a fractionation deviceused for proteins and/or peptides, which has any of thefollowing features:1) At least one portion of a substrate surface with whichproteins or the like are made in contact has an amount ofadsorption of bovine serum albumin of 50 ng/cm2 or less withrespect to the substrate surface, when a bovine serum albuminsolution is made in contact therewith.2) At least one portion of a substrate surface with whichproteins or the like are made in contact has an amount ofadsorption of human .beta.2-microglobulin of 3 ng/cm2 or less withrespect to the substrate surface, when a protein aqueoussolution consisting of human .beta.2-microglobulin and bovine serumalbumin is made in contact with the substrate surface.3) The fractionation device is provided with: a means forsupplying a solution containing proteins or the like； a meansfor separating proteins or the like from the solution； and ameans for concentrating proteins or the like in the solution,and in the fractionation device, at least one portion of thesubstrate surface with which proteins or the like are made incontact is subjected to a grafting process by using ahydrophilic polymer.By using the above-mentioned device, it becomes possibleto reduce non-peculiar adsorption of protein onto the substrate,and consequently to easily provide a sample from which proteinshaving high-molecular weights have been removed, and which isadvantageously used for an analysis.
